Down-the-hole rock drill with flushing fluid bypass control



March 25, 1969 DOWN-THE-HOLE ROCK DRILL WITH FLUSHING FLUID BYPASS CONTROL Filed Oct. ll, 1967 W- J- THOMAS ET L Law: A 0071/ March 25, 1969 w THOMAS ET AL 3,434,548

DO'NN-THE-HOLE ROCK DRILL WITH FLUSHING FLUID BYPASS CONTROL Sheet Filed Oct. 11, 1967 Mum/me;

W/l//9M J 77/0444: Iowa 6. 6077/? States US. Cl. 17318 7 Claims ABSTRACT OF THE DISCLOSURE In a down-the-hole drilling hammer there is a permanent restricted bypass for live actuating fluid from ahead of the valve chest to the drill bit and a second bypass which offers very low resistance to the flow of fluid, the second bypass being opened when the hammer is lifted off the bottom of the hole that is being drilled.

This invention relates to down-the-hole rock drills of the kind in which a hammer is so suspended at the end of a drill string that when the bit is off the floor of the hole being drilled, reciprocation of the bit is arrested while the full air stream flows down the hole for flushing purposes.

In a known appliance of the kind in question the hammer has a cylinder and a piston adapted to reciprocate within the cylinder. There is also a valve which serves for feeding air to either side of the piston to cause reciprocation. In addition the cylinder is connected to the drill string by means having lost motion with the valve or structure associated with the valve. When the means takes up the lost motion, a port to the top side of the cylinder is permanently opened and air passes through the cylinder to the exhaust ports while the piston is forced to the down position.

This known appliance has two drawbacks. The first is that no provision is made for air to bypass the cylinder during drilling. The only air available for flushing is the exhaust air. Secondly the means with lost motion has a part which retracts from a bore communicating with the cylinder. As the part moves back for normal drilling to be restored, it may chafe the bore and thus cause a permanent leakage of air into the back of the cylinder.

An object of the invention is to provide an appliance which allows for the passage of air past the cylinder during normal operation, and when the lost motion means takes up its lost motion a substantially complete bypass of all air is permitted.

In a down-the-hole drilling hammer comprising a cylinder, a piston receprocable in the cylinder, a chuck for securing a bit at the front end of the cylinder, valve means at the back end of the cylinder for controlling reciprocation of the piston, and drive means having axial lost motion with the cylinder for effecting a driving connection between the cylinder and a drill string and for conveying actuating fluid from the drill string to the controlling valve means, the present invention provides the improvement of a permanently open bypass for live actuating fluid from ahead of the valve means to the front end of the cylinder, and of a valve controlled by axial movement of the drive means, the latter valve being closed when the drive means is in its forward position relatively to the cylinder, and being open when the drive means is in its rearward position to open a bypass to the front end of the cylinder which offers such a low resistance to air flow as to subatent 3,434,548 Patented Mar. 25, 1969 stantially starve the controlling valve means of actuating fluid.

The invention is further discussed with reference to the accompanying drawings, in which:

FIGURE 1 is a longitudinal section through a part of a hammer,

FIGURE 2 is a part section of another embodiment, and

FIGURE 3 is a part section of a further embodiment.

The hammer illustrated in FIGURE 1 has a cylinder 2 connected to a drive shaft 3 with lost motion in the conventional way. The cylinder 2 is fitted with a cylinder liner 4 inside which a piston (not shown) reciprocates in the conventional manner under the control of a disc valve 5 held between two valve chest members 6 and 7.

The drive shaft 3 is hollow for conducting live air to the valve through passages 8 and is fitted with a spigot 9 which fits in a bore in the valve member 6. The spigot 9 differs from conventional spigots in that it has a blind bore 10. The walls of the spigot 9 are holed at two points. Firstly there are holes 11 of restricted cross-sectional area, and secondly there are holes 12 of large cross-sectional area. The member '6 is provided with a series of radial passages 13 leading from an annular recess 14. The passages 13 connect with a bypass 15 between the cylinder liner 4 and the cylinder 2.

During normal drilling the hammer parts are in the positions shown in the drawing. Air passes to the disc valve 5 via the passages 8 and also to the bypass 15 through the restricted apertures 11. Thus during normal drilling flushing air in excess of the exhaust air is available.

When the hammer is lifted, the drive shaft 3 takes up its lost motion and moves for such a distance that the apertures 12 register with the recess 14. NOW air inside the cavity of the drive shaft has unrestricted access to the bypass 15 and the effect is that the valve 5 is starved of air. It may be that enough air will get to the valve to cause gentle reciprocation of the piston, but this is no disadvantage.

In the embodiment illustrated in FIGURE 2 the holes 12 are omitted and the spigot 9 is open-ended so that the bore 10 is no longer blind. At the same time the valve member 6 is formed with a blind bore in which the spigot 9 operates. The lost motion of the drive shaft 3 is arranged to be of such an extent that the hammer can only be lifted from the floor of a drill hole when the end 16 of the spigot 9 clears the recess 14.

The spigot 9 of the drive shaft 3 is solid in the embodiment illustrated in FIGURE 3. In this case the permanent by-pass to the space 15 is provided from a space 17 fed by the passages 8, along bores 18 through the valve member 7 to an upper extension 19 of the space 15.

Once more the valve member 6 is formed with a blind bore. However, in this case the extent of the lost motion is arranged to be such that the end of the spigot 9 clears the bore in the member 6 before lifting takes place. The clearance is such that a free passage for air is provided down the bore in the member 6 to the passages 13.

In this latter case there may be some chafing between the spigot 9 and the bore in the member 6, but this has no deleterious effect, as it causes a slight increase of the by-pass air during normal drilling.

We claim:

1. In a down-the-hole drilling hammer comprising a cylinder, a piston reciprocable in the cylinder, a chuck for securing a bit at the front end of the cylinder, valve means at the back end of the cylinder for controlling reciprocation of the piston, and drive means having axial lost motion with the cylinder for effecting a driving connection between the cylinder and a drill string and for conveying actuating fluid from the drill string to the controlling valve means, the improvement of a permanently open bypass for live actuating fluid from ahead of the valve means to the front end of the cylinder, and of a valve controlled by axial movement of the drive means, the latter valve being closed when the drive means is in its forward position relatively to the cylinder, and being open when the drive means is in its rearward position to open a bypass to the front end of the cylinder which offers such a low resistance to air flow as to substantially starve the controlling valve means of actuating fluid.

2. The hammer claimed in claim 1 in which the permanent bypass is from a space ahead of and communicating with the controlling valve means to a bypass in the thickness of the cylinder wall.

3. The hammer claimed in claim 1 in which the drive means is a hollow shaft formed With a spigot at its front end, the spigot being adapted to slide in a valve bore with lateral ports giving access to a. bypass to the front end of the cylinder and the lateral ports being placed into communication with live actuating fluid by being uncovered by the spigot.

4. The hammer claimed in claim 3 in which the valve bore is blind and the spigot bore is open-ended, the spigot moving beyond the lateral ports when the drive means has taken up its lost motion.

5. The hammer claimed in claim 3 in which the spigot is solid and clears the valve bore when the drive means has taken up its lost motion.

6. The hammer claimed in claim 3 in which the spigot is formed with a blind bore which is in communication with the actuating fluid and formed with ports towards the closed end of the blind bore which ports register with the lateral ports when the drive means has taken up its lost motion.

7. The hammer claimed in claim 6 in which the permanent bypass is from the spigot bore through restricted ports in the spigot walls that register with the lateral ports during normal drilling.

References Cited UNITED STATES PATENTS 1,881,258 10/1932 Bayles 173-64 2,572,841 10/1951 Osgood et al. 173-58 3,169,584 2/1965 Stenuick 173-18 ERNEST R. PURSER, Primary Examiner.

U.S. Cl. X.R. 173-58, 64 

